Robotics and Human Augmented Systems

1. Introduction

2. Conceptualization and Theories

3. Summary

  

1. Introduction

The smart anthropomorphic contact surface technology (SACST) utilizes the soft contact model, normal force and pressure distribution at the contact interface, friction limit surface, and stiffness of contact to automatically adjust critical parameters of the contact interface, by measuring contact pressure distribution and dynamically reshaping the surface through embedded actuation systems in real time to redistribute or actively control the critical parameters in order to make a surface intelligent. Such design can also implement dynamic functions such as massage or tilting of contact surfaces. Also included in this framework is the use of MEMS microvalves and sensors for the research development of distributed contact surface. The miniaturization of MEMS valves makes it possible for the intelligent surface to become a distributed rather than a discrete one.

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2. Conceptualization and Theories

Figure 1. A schematic illustration of the smart anthropomorphic contact surface technology (SACST). The external contact source (Shape not shown) makes contact with the distributed contact surface blobs.

The schematic of such system is shown in Figure 1. In the figure, the distributed contact surface consists of the concatenation of actively controlled contact surface blobs. The mechanics of soft contact, therefore, is crutial in developing the framework. The individual surface is controlled by actuators via intelligent control algorithm with sensory information. The intire system communicates through a central information precessing and intelligent control unit.

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2.1 Modeling of anthropomorphic contact surface

Contact modeling between two linear elastic object was first derived by Hertz in 1882 with both theoretical and experimental results. This is later known as the Hertzian contact model. The model describes the contact behavior between two surfaces with a circular contact area as:

where a is the radius of contact, c is a propotional constant, and N is the normal force.

Based on the above observation, the power-law model for soft fingers was derived using the assumption of nonlinear elastic materials in contacts. The new theory for soft contacts, which subsumes the Hertzian contact model, is given in the following equation:

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2.2 Contact pressure distribution

The pressure distribution for a circular contact area with radius a can be written in the general form of

2.3 MEMS valves and sensor

Figure 2. Illustration of a transducer system

Figure 3. (left) SEM photo of the gate valve designs of rotary and linear actuations. (right) The packaged valve on quater coins.

Figure 4. The design spec of the MEMS valves and the measured flow rate of the gate valve design.

Figure 5. Typical relationships between the displacement of approach and the normal force for a hemisphere soft contact surface

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2.4 Implementation issues

Several implementtation issues in the research and development of the MEMS-based SACST system include the following:

Figure 10. A system with MEMS valves and zones of bladders. This schematic of the control system design shows the intelligent seat design with air pump, bladders zones, MEMS valves, sensors, and microprocessor control unit.

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3. Summary

Integrating the MEMS technology with contact theory and intelligent control technique, the SACST can alter behaviors of contact surfaces based upon robotics theories. To make SACST products more reliable and efficent, certain critical components are indispensable. For example, the MEMS valves should be able to work under more resistant force and with less power consumption; the contact sensor should have higher and flexible resolution; and the actuation mechanism of the bladders should become more integrated, more flexible and easier to be controlled. The next-genetion SACST technology will also integrate the intelligent operation system and control with actuators and sensors.

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Date revised - 04/08/2003